This invention relates generally to semiconductor infrared detectors and, more particularly, to techniques for suppressing gamma induced noise in semiconductor infrared detectors.
Semiconductor infrared detectors are commonly arranged in focal plane arrays and cryogenically cooled to very low temperatures to provide sensitive detection of infrared radiation for various types of space-based infrared sensor systems. Cooling these infrared detector arrays to very low temperatures is particularly important for highly sensitive detection of infrared radiation in the longer wavelength, or far infrared, portion of the spectrum, especially under low background conditions. However, low-temperature infrared detector arrays generate very small analog signals which are easily contaminated by noise, such as noise induced by high-energy gamma rays.
Gamma induced noise is a particular problem for space-based infrared sensor systems because the infrared detectors are continuously exposed to gamma ray emissions from the sun. These gamma emissions are filtered out by the earth's atmosphere and do not pose a problem for earth-based infrared sensor systems. However, both space-based and earth-based infrared sensor systems are susceptible to heavy gamma ray emissions from nuclear explosions.
Gamma ray emissions cause secondary or Compton electron generation within the infrared detector and neighboring semiconductor material, producing noise in the form of electrical pulses. These gamma induced pulses can severely degrade the detection capabilities of the infrared detector, and even cause total blindness in the case of nuclear explosions. Consequently, gamma pulse suppression is required in order to preserve highly sensitive detection of infrared radiation in a gamma ray environment.
One technique for suppressing gamma induced noise is pulse amplitude discrimination, which employs limited oversampling and extensive digital filtering to reduce the peak amplitude excursions of the detector signal. However, pulse amplitude discrimination does not completely eliminate gamma induced pulses from the detector signal, and it degrades the quality of the signal. Accordingly, there has been a need for an improved gamma suppression technique for semiconductor infrared detectors. The present invention is directed to this end.